Apparatus for manufacturing metal tube covered optical fiber cable and method therefor

ABSTRACT

An apparatus for manufacturing a metal tube covered optical fiber cable comprises an assembly of a plurality of roller pairs for forming a metal strip into a metal tube so that both side edge portions abut against each other, a laser (7) for welding the abutment portions with a laser beam to obtain a sealed metal tube (1c), an optical fiber guide for guiding an optical fiber (5) into the formed metal tube (1a), and a traction apparatus including a tension variable element for continuously drawing a sealed metal tube (id). The optical fiber guide is elastically urged against an inner wall opposite to an irradiated surface of the metal tube so that the optical fiber is protected even when the focal point of the laser beam is positioned below the abutment portions of the metal tube. In one embodiment a leaf spring mechanism is used to elastically urge the optical fiber guide.

This is a continuation, of application Ser. No. 07/730,915 filed Jul.29, 1991, now U.S. Pat. No. 5,210,391 issued May 11, 1993.

TECHNICAL FIELD

The present invention relates to an apparatus for manufacturing a metaltube covered optical fiber cable and a method therefor.

BACKGROUND ART

An optical fiber and a bundle of optical fibers are variously modifiedin accordance with the conditions under which they are used. However,tension member must be used with an optical fiber to assure a highstrength in some cases. When water permeates an optical fiber cable, itsstrength may be degraded. When an optical fiber cable is to be installedin the bottom of a sea or the bottom of the water, in order to assure asufficient installation tension and a high water resistance, an opticalfiber cable must be used in a jacket structure in which an optical fibercable is covered with a thin metal tube.

When an optical fiber cable having a small diameter tube is used, anoptical fiber is inserted into a metal tube having a longitudinal gap,and this gap is bonded by soldering.

According to this method, however, heat generated during bonding of thegap of the metal tube is applied to the optical fiber cable for arelatively long period of time to cause thermal damage.

In order to prevent this optical fiber cable from thermal damage, thereis provided an apparatus and method of welding abutment portions of ametal tube with a focused laser beam to continuously manufacture a metaltube covered optical fiber cable, as disclose in Published UnexaminedJapanese Patent Application No. 64-35514.

This apparatus for manufacturing the metal tube armored optical fibercable forms a continuously fed flat metal strip into a metal tube havinga longitudinal gap at a top portion. A guide tube is inserted into themetal tube through this gap of the metal tube, and an optical fiber isguided into the metal tube through the guide tube. After the gap of themetal tube having received this optical fiber is closed, the metal tubeis supplied to a laser welding unit.

The laser welding unit causes a guide roller to align the abutment edgeportions of the top portion of the metal tube to each other. A laserbeam having a focal point at a position outside the range of theabutment portions is radiated to weld the abutment portions. Since thelaser beam is focused outside the range of the abutment portions, theabutment portions can be welded without protecting the optical fiberwith a heat-shielding member.

This metal tube containing the optical fiber cable is drawn to have apredetermined outer diameter, and the drawn tube is continuously woundaround a capstan.

During drawing of this metal tube, an inert gas is supplied to the guidetube to carry the optical fiber cable by the viscosity resistance of thegas. While the metal tube is kept engaged with the capstan, the opticalfiber cable is blown outward against the inner surface of the metaltube, so that the length of the optical fiber cable is set larger thanthat of the metal tube. The optical fiber cable is not kept taut toprevent the optical fiber cable from stress caused by an installationtension or the like.

In order to protect the optical fiber cable from water entering from ahole formed in a damaged metal tube a gel is injected inside the metaltube. More specifically, after the optical fiber cable is blown outwardagainst the inner surface of the metal tube by the inert gas at thecapstan, the gel is injected from a gel guide tube different from theguide tube for guiding the optical fiber cable.

In the above conventional apparatus for manufacturing a metal tubearmored optical fiber cable, no heat-shielding member for protecting theoptical fiber is used at the time of welding of the abutment portions ofthe metal tube, and the position of the guide tube for guiding theoptical fiber cable is indeterminate. For this reason, the guide tube islocated near the abutment portions of the metal tube. Therefore heatgenerated during laser welding is undesirably applied to the opticalfiber cable to thermally damage the optical fiber cable. For example,when a temperature of the optical fiber cable near the abutment portionsduring laser welding is measured, a temperature near the optical fibercable is increased to at least about 600° C. For this reason, a finecrystal nucleus is formed and is grown to undesirably cause adevitrification phenomenon in which a scattering loss is increased.

Sputter components are produced during welding. When the guide tube isclose to the abutment portions, the sputter components deposited on theguide tube tend to be brought into contact with a rear bead of thewelded portion. When the sputter components are brought into contactwith the rear surface of the welded portion, the welded portion isthermally unbalanced to cause incomplete connection. In order to preventthis incomplete welding caused by the sputter components, whenproduction of the rear bead portion as a sputter source is suppressed, anonwelded portion is undesirably formed. When the guide tube is kept incontact with the abutment portions, the same phenomenon as in incompletewelding caused by the sputter components occurs. For these reasons, itis undesirably impossible to perform a continuous manufacturingoperation (operation for manufacturing a long cable) in practice.

When a radiation power density of a laser beam is excessively highduring laser welding, the metal tube is heated to a temperatureexceeding its melting point and is partially evaporated or removed toform a hole in an irradiated portion. In order to prevent this, a laserbeam is not conventionally focused within the range of the wallthickness of each abutment portion of the metal pipe, but is focusedabove the surface of the metal tube. When the laser beam is focusedabove the metal tube, the welded portion has a section in which thelower portion is sagged, so that a shrinkage hole and a crack tend to beformed inside the welded portion. In addition, an amount of sputtercomponents is also increased, resulting in inconvenience.

When the abutment portions of the metal pipe are to be welded with alaser beam, the metal tube is guided by the guide roller, so that theabutment portions are positioned with respect to the focal point of thelaser beam. During guiding of the metal tube along the guide roller, themetal tube tends to be fed in a zig-zag manner to degrade positioning ofthe abutment portions.

Optical fiber cables are used in a variety of application conditions andat various temperatures. The thermal expansion coefficient of the metaltube is much larger than that of the optical fiber cable. For thisreason, when optical fiber cables are used at high temperatures, atension acts on the optical fiber cable due to a difference inelongations of the metal tube and the optical fiber cable to damage theoptical fiber cable. This also occurs when a cable is installed at ahigh tension, e.g., in installment at the bottom of a sea.

To the contrary, when optical fiber cables are used at low temperatures,the optical fiber cable is brought into contact with the inner wallsurface of the metal tube having a large shrinkage amount due to a largedifference between the degrees of shrinkage of the metal tube and theoptical fiber cable. The optical fiber cable directly receives a sidepressure from the inner wall of the metal tube. Irregular bending forceshaving short periods act on the optical fiber cable to cause a so-calledmicrobend loss, thereby attenuating a signal transmitted through theoptical fiber cable.

In order to prevent damage and the like, the optical fiber cable isblown outward against the inner wall surface of the metal tube while themetal tube is kept engaged with the capstan, so that the length of theoptical fiber cable is set larger than that of the metal tube after thecable is straightened for use.

In this case, however, a difference between the length of the opticalfiber cable and the length of the metal tube (to be referred to as anextra length hereinafter) is determined by the outer diameter of thecapstan and a difference between the inner diameter of the metal tubeand the outer diameter of the optical fiber cable. The extra lengthcannot be arbitrarily controlled, and the optical fiber cable may bedamaged depending on application conditions.

As described above, while the metal tube is kept engaged with thecapstan, the optical fiber cable is blown outward against the innersurface of the metal tube by an inert gas to provide an extra length tothe optical fiber cable. For this reason, when a gel is to be injectedinto the metal tube, it must be injected while the optical fiber cableis kept blown outward against the inner wall of the metal tube due tothe following reason. That is, even if the gel is injected and then theinert gas is supplied, the gel causes resistance to fail to give theextra length to the optical fiber cable. When a gel is to be injected, agel guide tube is required in addition to the optical fiber cable andthe inert gas guide tube. Since these two guide tubes must besimultaneously inserted into the metal tube, the inner diameter of themetal tube is increased. In order to obtain a thin tube from this tube,the drawing amount is increased. Metal tubes may not be occasionallythinned in accordance with diameters of optical fiber cables, resultingin inconvenience.

SUMMARY DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above drawbacks, andhas as its object to provide an apparatus for manufacturing a metal tubecovered optical fiber cable and a method therefor, capable of preventingdamage to an optical fiber cable during welding abutment portions of ametal tube, capable of continuing the manufacturing operation for a longperiod of time, and capable of arbitrarily obtaining an extra length.

There is provided an apparatus for manufacturing a metal tube coveredoptical fiber cable, comprising an assembly, having a plurality ofroller pairs, for causing both side edges of a metal strip to abutagainst each other to form the metal strip into a metal tube, opticalfiber guiding means for guiding an optical fiber or an optical fiberbundle into the formed metal tube, laser welding means for radiating alaser beam to abutment portions of the metal tube to bond the abutmentportions to obtain a sealed metal tube, and drawing means forcontinuously drawing the metal strip, the formed metal tube, and thesealed metal tube incorporating the optical fiber or the optical fiberbundle through the assembly, the optical fiber guiding means, and thelaser welding means, characterized by comprising

tension adjusting means, arranged in the upstream of the assembly, forvariably adjusting a tension of the metal strip on an assembly side andadjusting a tension of the metal tube, and

tension adjusting means, arranged in the upstream of an optical fiberguide port in the optical fiber guiding means, for variably adjusting atension of the optical fiber cable,

the optical fiber guiding means being provided with a guide tube,inserted into the metal tube during formation thereof and elasticallyurged against an inner wall opposite to an irradiated surface of themetal tube at a radiation position of a laser beam, for guiding theoptical fiber or the optical fiber bundle into the metal tube, and

the traction means being provided with tension variable means forreducing a tension of the metal tube covered optical fiber cable.

The laser welding means is preferably arranged so that the laserradiation means positions a focal point of the laser beam to fall belowthe abutment portions of the metal tube.

A focal point shift amount (defocus amount) of the laser beam ispreferably determined to fall within a predetermined range determined bya laser beam power and a welding rate which does not produce a nonweldedportion.

The tension variable means is preferably constituted by a capstan aroundwhich the sealed metal tube is wound by a plurality of turns.

The laser welding means preferably comprises a guide shoe, located inrelationship to a metal tube path line and having a groove engaged withthe metal tube on one side, for positioning the abutment portions of themetal tube to the laser beam radiation position, and position adjustingmeans for finely adjusting the position of the guide shoe.

The inert gas supply tube or the gel guide tube is preferably connectedbetween the optical fiber guide port of the guide tube and a metal tubeinsertion portion.

The tension adjusting means for adjusting the tension of the metal tubeis preferably located in the downstream of the tension variable means.

There is provided a method of manufacturing a metal tube covered opticalfiber cable according to the present invention, comprising the formingstep of forming a metal strip to be formed into a metal tube, the laserwelding step of welding abutment portions of the metal tube to obtain asealed metal tube, the optical fiber guide step of guiding an opticalfiber or an optical fiber bundle in the metal tube, the traction step ofwinding the formed metal tube covered optical fiber cable, characterizedin that

a tension of the metal strip before the assembly step is set variable toadjust a tension of the metal tube, a tension of the optical fiber cablebefore the optical fiber guide step is set variable to adjust a tensionof the optical fiber cable guided into the metal tube, and the tensionsof the metal tube and the optical fiber cable are reduced in thetraction step to perform traction of the metal tube covered opticalfiber cable, and

in the optical fiber guide step, a guide tube is inserted into the metaltube at the laser beam radiation position where the guide tube is urgedagainst an inner wall opposite to the abutment portions of the metaltube, and the optical fiber or the optical fiber bundle is guided intothe metal tube through the guide tube.

In the laser welding step, the abutment portions of the metal tube arelocated at a predetermined position with respect to a laser beam focalposition by a guide shoe which is located in relationship to a path lineand has a groove engaged with the metal tube on one side.

The laser beam focal position is preferably set so that the laser beamis focused below the abutment portions of the metal tube.

The focus point shift amount of the laser beam is set to fall within apredetermined range determined by a power of the radiation laser beamand a welding rate which does not produce nonwelded portions, andwelding must be stably performed for a long period of time.

The guide tube is preferably inserted into the metal tube in which theoptical fiber cable is inserted, thereby supplying an inert gas or a gelthrough the guide tube.

According to the present invention, the optical cable is guided into thecovering metal tube by the guide tube also serving as a heat-shieldingmember. At the position where the guide tube is irradiated with thelaser beam, the guide tube is elastically urged against the metal tubeinner wall opposite to the abutment portions of the metal tube to reducea thermal influence on the optical fiber cable. At the same time, theoptical fiber cable is cooled by the inert gas blown into the guidetube.

Since the guide tube is located on the side opposite to the abutmentportions of the metal tube at the laser welding portion, a gap is formedbetween the abutment portions and the guide tube to assure a space wheresputter components produced during welding can be deposited.

When the abutment portions of the metal tube are to be welded with alaser beam, the metal tube is positioned while being urged by theengaging groove of the guide shoe and is guided while its zig-zagmovement is suppressed. In addition, the guide shoe position is finelyadjusted in correspondence with the focal position of the laser beam, sothat the abutment portions of the metal tube are accurately and stablypositioned. Furthermore, when the guide tube is to be located at aposition opposite to the abutment portions of the metal tube at thewelding portion, an elastic force acting on the guide tube can beincreased.

The focal position of the laser beam for welding the abutment portionsof the metal tube falls outside the abutment portions and is set insidethe metal tube. A welding width can be set almost constant and a rearbead width can be minimized while an excessive increase in radiationpower density of the laser beam can be prevented.

The focal point shift amount of the laser beam is set to fall within apredetermined range determined by the power of the radiation laser beamand the welding rate determined by the limit which does not producenonwelded portions. Therefore, the rear bead width can be uniformed, andinfluences of the sputter components can be suppressed.

By utilizing a difference between an elongation amount corresponding toa difference between the tension of the metal tube in the upstream ofthe tension variable means and the tension of the optical fiber cableguided into the metal tube, the length of the optical fiber cablerelative to the metal tube in the downstream of the tension variablemeans can be arbitrarily adjusted.

The tension variable means is preferably constituted by a capstan aroundwhich the sealed metal tube is wound by a plurality of turns. The numberof turns of the sealed metal tube wound around the capstan is changed toadjust the difference between the tension of the sealed metal tube onthe outlet side of the capstan and the tension of the optical fibercable in the metal tube to an arbitrary value.

When an inert gas or gel is to be guided into the metal tube, it can beguided through the guide tube which guides the optical fiber cabletherein. Only one guide tube is inserted into the metal tube, so that athin metal tube can be used, and the diameter of the metal tube can beeasily reduced in accordance with the diameter of the optical fibercable.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view of an overall arrangement showing an embodiment of thepresent invention,

FIGS. 2A and 2B are sectional views showing a metal tube in differentforming steps,

FIGS. 3A, 3B, and 3C are side views showing forming roller pairs of asecond assembly,

FIG. 4 is a view showing an arrangement of an optical fiber guide means,

FIG. 5 is a view showing an arrangement of a laser welding means,

FIG. 6 is a side view showing a guide shoe,

FIGS. 7A and 7B show a tension variable means and a tension adjustingmeans, respectively, in which FIG. 7A is a plan view thereof, and FIG.7B is a front view thereof,

FIG. 8 is a view showing abutment portions of a metal tube,

FIG. 9 is a graph showing a relationship between a tube outer diameterand a rear bead width,

FIG. 10 is a graph showing a relationship between a tube wall thicknessand a rear bead width,

FIG. 11 is a graph showing a relationship between a laser power and awelding rate,

FIG. 12 is a graph showing a relationship between a welding rate and afocal point shift amount,

FIGS. 13, 14, and 15 and FIG. 16 are views for explaining extra lengthcontrol operations,

FIG. 17 is a view showing a part of another layout of the optical fiberguide means,

FIG. 18 is a view showing part of another embodiment,

FIG. 19 is a view for explaining a leaf spring mechanism,

FIG. 20 is a view for explaining a state wherein a metal tube is movedupward,

FIG. 21A is a view for explaining a bent state of a guide tube,

FIG. 21B is a view for explaining a guide tube positioning mechanism,and

FIG. 22 is a view for explaining a metal tube positioning state at awelding position.

DETAILED DESCRIPTION

FIG. 1 is a view of an overall arrangement showing an embodiment of thepresent invention. As shown in FIG. 1, an apparatus for manufacturing ametal tube covered optical fiber cable comprises an assembly 2constituted by first and second assemblies 3 and 4 for forming a metalstrip 1 and forming the metal strip into a metal tube so as to abut bothside edges of the strip, an optical fiber guide means 6, arrangedbetween the first and second assemblies 3 and 4, for guiding an opticalfiber cable 5 into the formed metal tube, and a laser welding means 7arranged as the next stage of the assembly 2.

A measuring unit 8 and a drawing means 9 are arranged next to the laserwelding means 7. A traction means comprising a tension variable means 11and a tension adjusting means 13 for the metal tube covered opticalfiber cable 12 is arranged between the drawing means 9 and a cablewinding machine 10. The tension variable means 11, the tension adjustingmeans 13, and a tension adjusting means 14 for the metal strip 1 and atension adjusting means 15 for the optical fiber cables, which lattertwo are arranged in the upstream of the assembly 2, constitute an extralength control means for controlling a so-called extra length, i.e., thelength of the optical fiber cable relative to the metal tube. The firstassembly 3 constituting the assembly 2 comprise a plurality (e.g., five)of roller pairs 31a to 31e continuously aligned with each other. Theforming roller pairs 31a to 31e sequentially have different formingsurfaces and form the continuously fed metal strip 1 into asubstantially U-shaped metal tube 1a having a longitudinal gap at itstop portion, as shown in a sectional view of FIG. 2A.

Similarly, the second assembly 4 comprises a plurality (e.g., five) offorming roller pairs 41a to 41b continuously aligned with each other. Asshown in FIGS. 3A, 3B, and 3C, fins 17 gradually reduced in size areformed in the upper rollers corresponding to the forming roller pairs41a to 41d of the previous stages. A gap 16 of the metal tube 1a isengaged with each fin 17 so that the gap 16 is located at the top pointof the metal tube la and the gap 16 is gradually reduced by the fins 17.Abutment portions 18 of the metal tube 1a are brought into contact witheach other by the forming roller 41e of the last stage, thereby forminga metal tube 1b almost tightly closed at the abutment portions 18.

As shown in a partial sectional view of FIG. 4, the optical fiber guidemeans 6 comprises a guide tube 61 inserted into the metal tube 1b toguide the optical fiber cable 5, and an inert gas supply tube 63connected to the guide tube 61 through a tube connector 62 and an inertgas supply tube connector 62.

The guide tube 61 is made of a metal excellent in thermal conductivity,such as copper or a copper alloy. The outer diameter of the guide tube61 is smaller than the inner diameter of the metal tube 1b. The guidetube 61 is inserted from the gap 16 of the metal tube 1 between thefirst and second assemblies 3 and 4. A distal end of the guide tube 61passes through the laser welding means 7 and is located in front of aneddy current probe 81 of the measuring unit 8. The distal end of theguide tube 61 is inserted in front of the eddy current probe 81 asdescribed above because probe precision is adversely affected when theguide tube 61 reaches the eddy current probe 81.

When a probe measurement result is not adversely affected by insertionof the guide tube 61 passing through the eddy current probe 81, forexample, when the diameter of the metal tube is large and the guide tube61 is in contact with the inner wall surface of the metal tube at aposition opposite to a probe position, the guide tube 61 may be insertedand reaches a position passing through the position of the eddy currentprobe 81, that is, it may be inserted in front of the drawing means 9.

The guide tube 61 can be provided with leaf spring mechanism 611 (FIG.19) facing upward in front of and/or behind the laser beam radiationposition of the laser welding means 7 and elastically contacting theinner wall surface of the metal tube 1b or as shown in FIG. 20, themetal tube 1b can be located at a position higher by a predetermineddistance in front of and/or behind the laser beam radiation position.Alternatively, a downward elastic force can be applied to the guide tube61 itself to bring the guide tube 61 into contact with the inner wall ofthe metal tube 1b a position opposite to the laser beam radiationposition.

Elastic contact between the guide tube 61 and the inner wall of themetal tube 1b can be easily achieved, as shown in FIG. 21. The guidetube 61 is curved from a state I to a state II by elasticity of theguide tube 61 itself against the nature of straight extension of theguide tube 61 (FIG. 21(A)), the guide tube 61 is brought into contactwith the inner wall of the metal tube 1b in the state II (FIG. 21(B)),and the optical fiber guide means 6 is fixed at an appropriatelyposition to maintain a curved state. At this time, a positioningmechanism 612 constituted by a spring mechanism or the like ispreferably added to the optical fiber guide means 6, as needed.

When the metal tube 1b is to be located at a position higher by thepredetermined distance in front of the laser beam radiation position, apositioning unit 71 (to be described later) is finely adjusted. On theother hand, when the guide tube 61 is located at a position higher bythe predetermined distance behind the laser beam radiation position, asupport roll stand 82 (to be described later) is finely adjusted.

As shown in the arrangement of FIG. 5, the laser welding means 7comprises a positioning unit 71 for positioning the metal tube 1b and alaser welding unit 72.

The positioning unit 71 comprises, e.g., two sets of guide shoes 73 and74, a CCD seam monitor 75 arranged between the guide shoes 73 and 74,and micrometers 76 for finely adjusting vertical and horizontalpositions of the guide shoes 73 and 74.

The guide shoe 73 (74) comprises an upper shoe 73a (74a) and a lowershoe 73b (74b), as shown in the side view of FIG. 6. The upper shoe 73a(74a) has a flat surface which is brought into contact with the metaltube 1b. The lower shoe 73b (74b) has, e.g., a V-shaped groove engagedwith the metal tube 1b and is biased upward by a spring.

The laser welding unit 72 comprises a laser radiation means 77, and agas seal means 78 for sealing a welding position of the metal tube 1bwith an inert gas such as argon gas.

The laser radiation means 77 is connected to, for example, a carbondioxide laser device, guides and focuses a laser beam through an opticalsystem, and emits the focused laser beam on the surface of the metaltube 1b at an angle of about 90°. A focal point of the laser beamradiated on the surface of the metal tube 1b is adjusted to be locatedat a position below the abutment portions 18 of the metal tube 1b i.e.,a position inside the metal tube 1b.

The measuring unit 8 arranged next to the laser welding means 7comprises a support roll stand 82, a speedometer 83, and the eddycurrent probe 81 and checks a welded state or the like.

The drawing means 9 comprises a roller die and draws a welded and sealedmetal tube 1c to have a predetermined outer diameter, thereby obtaininga thin metal tube 1d corresponding to the outer diameter of the opticalfiber cable 5.

The tension variable means 11 arranged in the upstream of the drawingmeans 9 comprises a capstan having, e.g., a pair of rolls 11a and 11b,as shown in FIGS. 7A and 7B. The surface of one roll 11a is formedsmooth, and the surface of the other roll 11b has a plurality ofgrooves. The metal tube 1d is wound around the capstan withoutoverlapping the turns of the metal tube 1d. Similarly, the tensionadjusting means 13 comprises a dancer roll stand having a pair of rolls13a and 13b. One roll 13b is moved in a direction indicated by an arrowto change a distance between the rolls 13a and 13b so that the tensionis adjusted thereby adjusting a tension of the metal tube coveredoptical fiber cable 12 downstream of the capstan 11.

The tension adjusting means 14 and 15 for adjusting the tension of themetal strip 1 fed to the assembly 2 and the tension of the optical fibercable 5 supplied to the optical fiber guide inlet of the guide tube 61comprise dancer stands, respectively. The tensions of the dancer stands14 and 15 are variably adjusted by moving weights linked to pulleys 14aand 15a engaged with the metal strip 1 and the optical fiber cable 5.

An operation of manufacturing the metal tube covered optical fiber cable12 by the manufacturing apparatus having the above arrangement will bedescribed in an order of manufacturing steps.

(1) Forming Step

The metal strip 1 is continuously supplied while the metal strip 1 isadjusted by the dancer stand 14 to have a predetermined tension. Thefirst assembly 3 of the assembly 2 forms the supplied metal strip 1 intothe metal tube 1a having the longitudinal gap 16 at the top portion. Themetal tube 1a is supplied to the second assembly 4, and the gap 1a issequentially engaged with the fins 17 of the forming roller pairs 41a,41b and is gradually reduced. The gap 16 is eliminated by the formingroller pair 41e of the last stage, so that the abutment portions 18 areperfectly closed, thereby obtaining the metal tube 1b. When the metaltube 1b passes through the last forming roller pair 41e, a small gap 18a(to be described later) is actually formed between the abutment portions18. The gap 18a was not changed in a path from the forming roller pair41e to the laser beam radiation position, as detected by an another CCDmonitor (not shown).

(2) Optical Fiber Cable Insertion Step

Meanwhile, the optical fiber cable 5 adjusted by the dancer stand 15 tohave a predetermined tension is continuously supplied through the guidetube 61 which has been inserted from the gap 16 of the metal tube 1abetween the first and second assemblies 3 and 4. At the same time, argongas is supplied to the guide tube 61 from the inert gas supply tube 63connected to the guide tube 61.

(3) Laser Welding Step

The metal tube 1b inserted into the guide tube 61 is supplied to thelaser welding means 7. Since the metal tube 1b supplied to the laserwelding means 7 is positioned by the fins 17 of the forming roller pairs41a and 41b, the abutment portions 18 can be perfectly aligned with theposition of the laser beam emitted from the laser beam radiation means77.

The metal tube 1b supplied to the positioning unit 71 of the laserwelding mean 7 is engaged with and guided along the grooves of the guideshoes 73 and 74. Lateral shifts, rotation and zig-zag movement of themetal tube 1b can be prevented. The positional deviations of theabutment portions 18 were observed on the CCD monitor 75. When a guideroller was used, the abutment portions 18 were moved within the range of±100 μm due to torsion. However, when the guide shoes were used, theabutment portions were moved by only ±15 μm.

Subsequently, the CCD seam monitor 75 continuously detects the positionsof the abutment portions 18 of the metal tube 1b, and the micrometer 76is automatically or manually operated in accordance with a detectionresult to move the guide shoes 73 and 74, thereby finely adjusting thatthe abutment portions 18 are located at a predetermined position withrespect to the focal point of the laser beam.

The role of the positioning unit 71 will be described below. Aspreviously described, the guide shoes 73 and 74 in the positioning unit71 prevent rotation and zig-zag movement of the metal tube 1b and guide,to the laser beam radiation position, the abutment portions 18accurately positioned by the rollers 41a to 41d with fins with respectto the laser radiation position without causing zig-zag movement of themetal tube 1b. As previously described, it is possible to move the metaltube 1b upward by a predetermined distance in front of the laser beamradiation position upon adjustment of the positioning unit 71. As aresult, elastically tight contact between the guide tube 61 and theinner wall surface of the metal tube 1b can be performed to minimize anadverse influence of laser welding (to be described later) and allow acontinuous manufacturing operation for a long period of time.

As shown in FIG. 22, the positioning unit 71, i.e., the metal tube 1b ismoved upward or downward by a predetermined distance or more (within thelimit of elasticity) with respect to a path line by using the supportrolls 82a and 82b of the support roll stand 82 and the final formingroller pair 41e as two support points, so that the metal tube 1bconstitute two sides of a substantial triangle.

At this time, a light tension acts on the metal tube 1b located betweenthe support roll stand 82 and the final forming roller pair 41e. Thisindicates that the positioning unit 71 also serves as a means foradjusting a tension of the metal tube (particularly 1c and 1d ) as inthe tension adjusting means 14 for the metal strip (to be described indetail later). Vibrations of the metal tube 1b at the laser weldingposition (marks X in FIG. 22) can be suppressed.

In practice, another CCD monitor (not shown) was located at a positioninclined from the laser radiation position by 90° with respect to theCCD seam monitor 75 and the path line as the center, and verticalvibrations of the metal tube 1b were observed. As a result, when theguide shoes 73 and 74 in the positioning unit 71 are open, the metaltube 1b was vibrated in the range of about ±100 μm to about ±150 μm.However, when the metal tube 1b was fixed by the guide shoes 73 and 74,the metal tube 1b was vibrated within the range of about ±20 to about±30 μm. When the positioning unit 71 is adjusted as indicated by a state(A) or (B) in FIG. 22, the metal tube 1b was confirmed to be vibratedwithin the range of about ±5 μm.

When the elastic contact between the guide tube 61 and the inner wallsurface of the metal tube 1b is taken into consideration, thepositioning unit 71 is more preferably adjusted in the state (A) thanthe state (B).

With the above adjustment operations, highly precise welding control canbe performed, adverse welding influences can be minimized, a long-termoperation is allowed.

The metal tube 1b having abutment portions 18 whose positions areadjusted is supplied to the laser welding unit 72. The laser weldingunit 72 radiates a laser beam from the laser radiation means 77 to weldthe abutment portions 18 while supplying argon gas from the gas sealmeans 78 to the abutment portions 18 of the metal tube 1b. The innersurface of this welded portion is sealed by argon gas flowing within theguide tube 61 and reversely flowing from the distal end of the guidetube 61.

Before and after the laser beam radiation position, the guide tube 61which guides the optical fiber cable 5 is located in elastic contactwith the inner wall of the metal tube 1b at a position opposite to thelaser beam radiation position, and a gap is formed between the innersurfaces of the abutment portions 18 and the guide tube 61. The opticalfiber cable 5 is shielded from heat by means of this gap and the guidetube 61, thereby minimizing the thermal influence on the optical fibercable 5. In addition, the optical fiber cable 5 is cooled by the argongas flowing in the guide tube 61 and the argon gas reversely flowingfrom the guide tube 61, thereby minimizing a temperature rise of theoptical fiber cable 5.

For example, when the guide tube 61 was in contact with the abutmentportions 18 at the laser radiation position, the temperature near theoptical fiber cable 5 heated to a temperature of 600° C. or more canbecome about 115° C. to about 135° C. due to the presence of the gap.When argon gas flowed in the guide tube 61, the temperature was furtherreduced to about 100°C.

When the above gap is formed, an adverse influence on welding, which iscaused by sputter components deposited on the guide tube 61, can belagged. Therefore, welding can be stably performed for a long period oftime.

Since the laser beam emitted from the laser radiation means 77 isadjusted so that the focal position of the laser beam is set inside themetal tube 1b, an excessive increase in power density of the laser beamincident on the abutment portions 18 can be prevented, and stablewelding can be performed.

When the focal position is focused inside the metal tube 1b, and once acavity is formed, a beam reflected by a cavity wall is focused towardthe bottom of the cavity, so that a deep cavity is formed. A weldingwidth can be set to be almost constant, and a rear bead width can bemade small.

When the focal point shift amount of the laser beam is set to be apredetermined value, the rear bead width can be reduced, and sputterinfluences can be suppressed.

A minimum value b_(min) of the rear bead width is determined by acondition that nonwelded portions are not left in the abutment portions18. A maximum value b_(max) of the rear bead width is determined by thelimit in which sputter influences do not occur in a long-term operation.

Although the metal tube 1b is held by the guide shoes 73 and 74 at theposition of the laser welding means 7, the small gap 18a is formedbetween the abutment portions 18 of the metal tube 1b by a spring backat the position of the laser welding portion 72, as shown in FIG. 8. Thespring back which forms this small gap is influenced by rigidity of themetal tube 1b, i.e., an outer diameter d of the formed metal tube 1b.For example, a relationship between the outer diameter d (mm) and therear bead width b (μm) is examined and shown in FIG. 9 when a laser beamhaving a power of 400 (w) is incident in the small gap 18a while themetal tube 1b consisting of Fe-group stainless having a longitudinalmodulus of elasticity of 18,000 (kg/cm²) is perfectly fixed. The tubeouter diameter d is plotted along the abscissa in FIG. 9, and the rearbead width b is plotted along the ordinate. Referring to FIG. 9, acircle indicates a portion where a nonwelded portion is not formed, anda cross indicates a portion where a nonwelded portion is formed.Therefore, a straight line A indicates the limit at which nonweldedportions are not formed. The straight line A is given as b=10d.

In an actual apparatus, according to the observation with the CCD seammonitor 75, a relative vibration of about ±5 (μm) was found to occurbetween the laser beam and the small gap 18a due to small vibrations ofthe apparatus.

The minimum width b_(min) of the rear bead becomes 10d±5 (μm). Forexample, when the outer diameter of the metal tube 1b is 1 (mm), theminimum width b_(min) of the rear bead becomes 20 (μm).

The minimum width b_(min) =10d±5 of the rear bead is exemplified withuse of the metal tube 1b consisting of Fe-group stainless having thelongitudinal modulus of elasticity of 18,000 (kg/mm²). However, whenFe-group stainless or an Ni-group alloy having a longitudinal modulus ofelasticity of more than 18,000 (kg/mm²) is used, the rear bead width isset to be larger than the minimum width b_(min), and good welding freefrom the nonwelded portions can be performed.

The limit free from the sputter components even in a long-term operationis determined by a shape of a welding portion. A relationship between atube wall thickness t (mm) and the rear bead width b (μm) is shown inFIG. 10 when a laser beam having a power of 400 (w) is emitted in thesmall gap 18a to perform welding. The tube wall thickness t is plottedalong the abscissa of FIG. 10, and the rear bead width is plotted alongthe ordinate. Referring to FIG. 10, a circle indicates a state whereinno sputter influence is found and welding can be continuously performedfor a long period of time, e.g., 10 hours. A cross indicates a statewherein the sputter influence occurs and welding cannot be performed fora long period of time. The long period of time, i.e., 10 hourscorresponds to a maintenance timing in an actual operation. This timedoes not indicate the limit time free from the sputter influence.

A straight line B indicates the limit free from the sputter influenceeven in an operation for a long period of time and is represented byb=1000(t/2), when the tube wall thickness t is 0.1 (mm), an allowablemaximum width b_(min) of the rear bead width can be 50 (μm).

As described above, when the laser beam having a power of 400 (w) isused, and the metal tube 1b has a wall thickness of 0.1 (mm) and anouter diameter of 1 (mm), the width b of the rear bead is controlled tofall within the range of 20 to 50 (μm) to perform welding. The sputterinfluence can be suppressed even if welding is performed for a longperiod of time. Therefore, welding free from defects can be continuouslyperformed.

Since the minimum value b_(min) of the rear bead width is determinedunder the condition that nonwelded portions are not left in the abutmentportions 18, the minimum value is determined by an output density of alaser beam incident on the metal tube 1b. This output density isassociated with a welding rate V. The power P of the laser beam and thewelding rate V are changed to perform welding in a condition where theminimum value b_(min) is larger than or equal to about 10d±5 (μm), andin a condition that the minimum value is smaller than 10d±5 (μm). Thesetest results are shown in FIG. 11. The laser power P (W) is plottedalong the abscissa, and the welding rate V (m/min) is plotted along theordinate in FIG. 11. Referring to FIG. 11, a circle indicates a casewhich satisfies the above condition, and a cross indicates a case whichdoes not satisfy the above condition. This limit is indicated by astraight line C.

The limit free from the sputter influence in an operation for a longperiod of time is associated with a welding depth, i.e., a laser beamfocal point shift amount (defocus amount). The welding rate V and afocal point shift amount F (absolute value) are changed to performwelding in a condition that the maximum value b_(max) of the rear beadwidth is equal to or smaller than 1000(t/2) and in a condition that themaximum value is larger than 1000(t/2). The test results are shown inFIG. 12. The welding rate V (m/min) is plotted along the abscissa inFIG. 12, and the focal point shift amount F (mm) is plotted along theordinate. Referring to FIG. 12, a circle indicates a case whichsatisfies the above condition, and a cross indicates a case which doesnot satisfy the above condition. This limit is indicated by a straightline D.

For example, when a laser beam having a power of 400 (w) is used, amaximum welding rate V_(max) for welding free from nonwelded portions is4 (m/min) from FIG. 11. A minimum value of the focal point shift amountF free from the sputter influence at this welding rate is 2 (mm) fromFIG. 12. When the laser power P is 400 (W), the welding rate V is set to4 (m/min) and the focal point shift amount F is set to 2 (mm), long-termwelding free from the sputter influence can be performed while the rearbead width b is kept small.

The small gap 18a between the abutment portions 18 of the metal tube 1bis slightly changed in accordance with an extra length control conditiondescribed separately and the method of setting the positioning unit 71(A and B in FIG. 22). For example, when the state A in FIG. 22 is set,the size of the small gap 18a is increased. However, when the state B inFIG. 22 is set, the size tends to be reduced.

In practice, within the measurement mesh range of the presentapplication, however, an influence of a change in the small gap 18a wasfound to rarely influence the welding result.

(4) Measurement and Drawing Step

The sealed metal tube 1c having the welded abutment portions 18 by focalshift (defocusing) welding, as described above, is supplied to themeasurement unit 8. In the measurement unit 8, the passing speed, i.e.,the welding rate V, of the metal tube 1c is measured by the speedometer83 while the metal tube 1c is supported by the support roll stand 82.The welded state is checked by the eddy current probe 81.

The metal tube 1c passing through the eddy current probe 81 is drawn bythe drawing means 9 to have a diameter corresponding to the outerdiameter of the optical fiber cable 5 incorporated in the metal tube 1cthereby obtaining the metal tube covered optical fiber cable 12. Duringdrawing of the metal tube 1c by the drawing means 9, since only oneguide tube 61 is inserted into the metal tube 1c just at the inlet sideof the eddy current probe 81 and since the guide tube 61 does not extendup to the drawing means 9, the metal tube 1c can be made thin, and thediameter of the metal tube 1c can be easily reduced.

(5) Traction and Winding Step

The metal tube covered optical fiber cable drawn by the drawing means 9is wound by the cable winding machine 10 through the tension variablemeans 11 and the tension adjusting means 13.

When the metal tube covered optical fiber cable 12 is to be wound, thesealed and diameter-reduced metal tube 1d must be engaged with theoptical fiber cable 5. For this purpose, prior to a continuousoperation, after the welded and sealed metal tube 1d is manually woundaround the capstans 11a and 11b of the tension variable means 11 by aplurality of times, it is subjected to traction. The distal end of themetal tube 1d is mounted on the cable winding machine 10 through thetension adjusting means 13. In this state, the distal end of the opticalfiber cable 5 is inserted just in front of the capstan 11a, and themetal tube 1d is pressed at this position, thereby engaging the opticalfiber cable 5 with the inner wall of the metal tube 1d. Thereafter themetal tube 1d is wound while the capstans 11 are driven. The opticalfiber cable 5 together with the metal tube 1d is pulled from the guidetube 61, thereby winding the pulled product as the metal tube coveredoptical fiber cable 12. In the case where the optical fiber cable 5 andthe metal tube 1d can be wound together around the capstan 11a, it isnot necessary to engage the optical fiber cable 5 with the metal tube 1dby pressing that tube.

(6) Extra Length Control Step

When the metal tube covered optical fiber cable 12 is wounded around thecapstans 11a and 11b and is subjected to traction, a tension acts due toa frictional force between the metal tube 1d of the metal tube coveredoptical fiber cable 12 and the capstans 11a and 11b. This frictionalforce is large at the initial period of winding and is graduallyreduced. The tension is also large at the initial period of winding andis gradually reduced, accordingly. Elongation occurs in a wound portionof the metal tube 1d in correspondence with the tension.

Assume that, in a normal operation, the stainless steel strip 1 having awidth of 4 mm and a thickness of 0.1 (mm) is used, that the strip 1 isformed into a metal tube 1c having an outer diameter of 1.3 (mm), andthat the metal tube 1c is drawn into the metal tube 1d having an outerdiameter of 1.0 (mm). In this case, when a tension of the metal strip 1is adjusted by the tension adjusting means 14 such that a tension of themetal tube 1c at the inlet of the capstan 11a is set to about 20 (kgf),the tension causes elongation of the metal tube 1d by +0.30%. At thistime, when the tension of the optical fiber cable 5 having an outerdiameter of 125 (μm) is adjusted by the tension adjusting means 15 and atension of about 25 (gf) acts on the inlet side of the capstan 11a,elongation occurs by +0.03%.

Degrees of elongation of the metal tube 1d and the optical fiber cable 5are measured as a function of the number of turns of the metal tube 1dwound around the capstans 11a and 11b. The measurement results are shownin FIG. 13. The number of turns of the tube wound around the capstans11a and 11b is plotted along the abscissa, and an elongation (%) of themetal tube 1d is plotted along the ordinate. Referring to FIG. 13, acurve E represents characteristics of changes in elongation of the metaltube 1d, and a curve F represents characteristics of changes inelongation of the optical fiber cable 5. As indicated by the curve E,when the metal tube 1d is wound around the capstans 11a and 11b sixtimes, the final elongation of the metal tube 1d supplied to the tensionadjusting means becomes very small. As indicated by the curve F, whenthe optical fiber cable 5 is wound one and a half times, elongation isalmost zero.

When the elongation of the optical fiber cable 5 becomes almost zero byits 1.5-time winding, an elongation of +0.19 is present in the metaltube 1d. Immediately after the metal tube 1d is wound around thecapstans 11a and 11b six times, the tension of the metal tube 1d becomesalmost zero. In this case, the elongation of the metal tube 1d becomesalmost zero accordingly. That is, when the tube wound around thecapstans six times, the metal tube 1d shrinks by 0.19% as compared with1.5-time winding. On the other hand, since the tension of the opticalfiber cable is almost zero upon 1.5-time winding, no change inelongation occurs, and the length of the optical fiber cable is keptunchanged. For this reason, 6-time winding causes an elongation of 0.19%in the optical fiber cable 5 as compared with the metal tube 1d.

The winding diameter of the metal tube 1d wound around the capstans 11aand 11b is different from that of the optical fiber cable 5 engaged withthe inner wall of the metal tube 1d. For this reason, when the diameterof each of the capstans 11a and 11b is about 500 mm, the optical fibercable 5 has an elongation amount corresponding to +0.09% with respect tothe metal tube 1d. This elongation amount of 0.09% is canceled with theabove 0.19%. As a result, the optical fiber cable 5 is longer than themetal tube 1d by 0.10%.

Assume that the tension of the metal tube 1d at the inlet side of thecapstan 11a is the same as that shown in FIG. 13, and that the tensionof the optical fiber cable 5 is changed to increase the tension at theinlet side of the capstan 11a. In this case, a change in elongation ofthe optical fiber cable 5 is indicated by curve F1 in FIG. 14. When theoptical fiber cable 5 is wound around the capstans 11a and 11b 3.5times, the tension is almost zero. On the other hand, the elongation ofthe metal tube 1d is 0.09% in 3.5-time winding. When the elongation of0.09% of the metal tube 1d is canceled with the elongation of 0.09% ofthe optical fiber cable 5, a difference between the lengths of thesemembers, i.e., an extra length, becomes 0%.

Contrary to the case in FIG. 14, when a tension of the metal tube 1d atthe inlet side of the capstan 11a is increased by applying a tension ofthe metal strip 1 by the tension adjusting means while the tension ofthe optical fiber cable 5 at the inlet of the capstan 11a is keptunchanged, a change in elongation in metal tube 1d is represented by acurve E1 in FIG. 15.

Assume that the tension of the metal tube 1d at the inlet side of thecapstan 11a is set equal to that in FIG. 13, and that a tension of themetal tube 1d at the outlet sides of the capstans 11a and 11b areincreased by the tension adjusting means 13. In this case, a change inelongation of the metal tube 1d is represented by a curve E2 in FIG. 15.A curve E3 in FIG. 15 represents a case wherein the tensions of themetal tube 1d at the inlet and outlet sides of the capstans 11a and 11bare increased.

As described above, one or both of the tensions of the metal tube 1d atthe inlet and outlet sides of the capstans 11a and 11b are increased, orboth the tensions are increased by a predetermined value. In this case,the length of the optical fiber cable 5 can be larger than that of themetal tube 1d by a desired amount. For example, as indicated by thecurve E3, when the metal tube 1d is wound around the capstans 11a and11b by one and half times, the elongation of the metal tube 1d becomes+0.26%. Even if the elongation of 0.09% of the optical fiber cable 5,which is caused by the winding diameter, is subtracted from theelongation of the metal tube 1d, the optical fiber cable 5 is longerthan the metal tube 1d by 0.17% at the outlet side of the capstan.

When a tension of the optical fiber cable 5 at the inlet side of thecapstan is set larger than that in FIG. 14, and a change in elongationof the optical fiber cable 5 is represented by a curve F2 in FIG. 16,the length of the optical fiber cable 5 can be set smaller than that ofthe metal tube 1d. In this case, the elongation of the optical fibercable 5 becomes almost zero in 5-time winding, and the correspondingelongation of the metal tube 1d becomes +0.04%. This elongation of+0.04% is subtracted from the winding difference of 0.09% in the opticalfiber cable 5. Therefore, the optical fiber cable 5 can be set shorterthan the metal tube 1d by 0.05%.

As described above, by systematically adjusting the capstans 11a and 11bwound with the metal tube covered optical fiber cable 12 by a pluralityof times, the tension adjusting means 14 for the metal strip 1, and thetension adjusting means 15 for the optical fiber cable 5, andoccasionally the tension adjusting means 13 in the downstream of thecapstans 11a and 11b, the length of the optical fiber cable 5 relativeto the metal tube 1d can be arbitrarily adjusted. When the tensions ofthe metal tubes 1c and 1d are adjusted by adjusting the positioning unit71 as in the tension adjusting means 14 for the metal strip 1, extralength control can be more precisely performed. In this case, the extralength control function of the positioning unit 71 is the same as thatof the tension adjusting means 14 of the metal strip, and a detaileddescription thereof will not be made.

As described above, the metal tube covered optical fiber cable 12 ismanufactured while the extra length is controlled to a predeterminedlength.

In the above embodiment, argon gas is used as an inert gas. However,nitrogen gas may be used to obtain the same effect as described above.

In the above embodiment, a gel is not supplied to a metal tube forcovering the optical fiber cable. When the gel is supplied to the metaltube, a gel is supplied from the insert gas supply tube 63 in theoptical fiber cable guide means 6. In this manner, the gel can besupplied to the metal tube 1d by utilizing only one guide tube 61.

In this case, the inert gas and gel are supplied at a pressure whichdoes not apply a tension on the optical fiber cable 5 by the inert gasor gel flow because insertion of the optical fiber cable 5 and extralength control can be achieved, as they are desired, without supplyingthe inert gas and gel through the optical fiber cable guide means 6.

In the above embodiment, the optical fiber cable guide means 6 isarranged between the first and second assemblies 3a and 4 of theassembly 2. However, as shown in FIG. 17, the optical fiber cable guidemeans may be arranged at the inlet of the first assembly 3, and theguide tube 61 may be inserted at the inlet of the first forming rollerpair 31a.

In the above embodiment, the traction means comprising the capstans 11aand 11b of the direct tension variable means 11 and the tensionadjusting means 13 is arranged in the downstream of the drawing means 9,and the tensions of the optical fiber cable 5 at the inlet and outletsides of the capstans 11a and 11b and the tension of the optical fibercable at the inlet side of the capstans are adjusted by the capstans 11aand 11b and the tension adjusting means 14, 15, and 13 while traction ofthe metal tube covered optical fiber cable 12 is kept performed, therebyperforming extra length control. However, as shown in FIG. 18, a pullingmeans 19 for pulling the metal tube 1d may be arranged at the inletsides of the capstans 11a and 11b in the traction means to arbitrarilyadjust the tension of the metal tube 1d at the inlet side of thecapstans.

For example, an endless capstan may be used as the pulling means 19, andthe metal tube 1d is pulled while being clamped between the endlesscapstans, so that the metal tube 1d can be pulled with a tensionrequired in a forming schedule. By adjusting a feed speed of the endlesscapstan, the tension of the metal tube 1d supplied to the capstan 11acan be arbitrarily controlled.

For example, when the length of the optical fiber cable 5 is set smallerthan that of the metal tube 1d, in the case of FIG. 16, since a tensionof the metal tube 1d at the inlet side of the capstan 11a cannot bereduced due to a forming schedule, a tension of the optical fiber cable5 at the inlet side is increased. However, an excessive increase intension of the optical fiber cable is not preferable. A tension of themetal tube 1d at the inlet side is decreased to obtain an effect whereina tension of the optical fiber cable 5 is relatively increased.Therefore, the length of the optical fiber cable 5 can be reducedwithout applying an excessive force to the optical fiber cable 5.

After the metal tube covered optical fiber cable 5 is manufactured andis to be fabricated in the subsequent process, an actual extra lengthmay become different from a target extra length. In this case, extralength control is also required. When the extra length control isperformed in advance in consideration of a deviation in extra lengthvalue, a metal tube covered optical fiber cable having an optimal extralength after the subsequent fabrication can be obtained.

In each embodiment described above, one optical fiber cable is insertedinto a metal tube. However, an optical fiber bundle consisting of aplurality of optical fibers can also be guided into a metal tube in thesame manner as described above.

As described above, according to the present invention, an optical fibercable is guided into a metal tube by a guide tube also serving as aheat-insulating member, and the guide tube is brought into contact withthe inner wall of the metal tube at a position opposite to the abutmentportions of the metal tube. The optical fiber cable can be cooled by aninert gas blown into the guide tube. An increase in temperature of theoptical fiber cable at the laser welding portion of the metal tube canbe suppressed, and thermal damage to the optical fiber cable can beprevented. Therefore, a high-quality metal tube covered optical fibercable can be manufactured.

The guide tube is located in the laser welding portion at a positionopposite to the abutment portions of the metal tube, and a gap is formedbetween the abutment portions and the guide tube so that a space inwhich sputter components produced during welding can be deposited can beassured. Therefore, the metal tube can be continuously welded for a longperiod of time.

When the abutment portions of the metal tube are to be welded, the metaltube is held and positioned by the engaging groove of each guide shoe,and the guide shoe position can be finely adjusted in correspondencewith the focal position of the laser beam. Therefore, since the abutmentportions of the metal tube can be accurately positioned, the abutmentportions of the metal tube can be highly precisely welded.

The focal position of the laser beam for welding the abutment portionsof the metal tube is shifted outside the range of the abutment portionsand is moved inside the metal tube, an excessive increase in radiationpower density of the laser beam can be prevented, and at the same timethe welding width can be set almost constant. Therefore, welding freefrom defects in the abutment portions of the metal tube can beperformed.

The focal point shift amount of the laser beam is given as apredetermined value determined by the power of the radiation laser beamand the welding rate determined not to produce nonwelded portions. Therear bead width can fall within the predetermined range accordingly, andproduction of sputter components can be suppressed. Therefore, anoperation can be stably performed for a long period of time.

The tensions at the inlet and outlet of the capstans serving as thetension variable means can be adjusted by the tension of the metal stripformed into a metal tube, and the tension of the metal tube coveredoptical fiber cable to cause a difference between the tension of thesealed metal tube wound around the capstans and the tension of theoptical fiber cable incorporated in the metal tube. Therefore, thelength of the optical fiber cable relative to the metal tube can bearbitrarily adjusted in accordance with application conditions, and themetal tube covered optical fiber cable can be stably installed and used.

When a gel is to be supplied in the metal tube, it can be suppliedthrough the guide tube which guides the optical fiber cable, only oneguide tube is inserted into the metal tube. A small-diameter metal tubecan be used, and the diameter of the metal tube can be easily reduced incorrespondence with the diameter of the optical fiber cable.

Further, the guide tube can be easily drawn, since the guide tube doesnot extend up to the drawing means.

We claim:
 1. An apparatus for manufacturing an optical fiber cablecovered with a metal tube, comprising:tube forming means for forming ametal sheet into an unsealed metal tube having abutment portions ofabutting side edges of the metal tube for sealing said metal tube; andoptical fiber guide means for guiding at least one optical fiber intosaid unsealed metal tube while said unsealed metal tube is maintainedunder traction; said optical fiber guide means comprising a guide tubeinserted into said unsealed metal tube for guiding said at least oneoptical fiber into said metal tube and for protecting said at least oneoptical fiber; welding means for welding said abutment portions of saidmetal tube, with the optical fiber guide means therein, for sealing saidmetal tube; and said guide tube being provided across a welding positionof said welding means.
 2. The apparatus of claim 1, wherein said atleast one optical fiber comprises an optical fiber bundle.
 3. Theapparatus of claim 1, wherein said optical fiber guide means furthercomprises an inert gas tube connected between an inlet port of the atleast one optical fiber and a metal tube insertion port.
 4. Theapparatus of claim 1, wherein said optical fiber guide means furthercomprises a filler tube connected between an inlet port of the at leastone optical fiber and a metal tube insertion port.
 5. The apparatus ofclaim 1, wherein said welding means comprises laser welding means. 6.The apparatus of claim 5, wherein said welding means is positioned tocause a focal point of a laser beam thereof to fall below abutmentportions of said metal tube which are to be welded.
 7. The apparatus ofclaim 6, wherein a focal point shift amount of said laser beam isdetermined to fall within a predetermined range determined by a laserbeam power and a welding rate which does not produce a non-weldedportion.
 8. The apparatus of claim 5, wherein said welding meanscomprises position adjusting means for positioning said abutmentportions of said metal tube to a predetermined position with respect toa laser beam radiation position and a path line of said metal line. 9.The apparatus of claim 1, further comprising position adjusting meansfor adjusting the position of said guide tube relative to said weldingposition of said welding means.
 10. An apparatus for manufacturing anoptical fiber cable covered with a metal tube, comprising:welding meansfor welding abutment portions of abutting side edges of a metal tube toseal said metal tube; and optical fiber guide means for guiding at leastone optical fiber into said metal tube while said metal tube ismaintained under traction, said optical fiber guide means comprising aguide tube inserted into said metal tube for guiding said at least oneoptical fiber into said metal tube; said guide tube being providedacross a welding position of said welding means; and said optical fiberguide means further comprising an inert gas tube connected between aninlet port of the at least one optical fiber and a metal tube insertionport.
 11. An apparatus for manufacturing an optical fiber cable coveredwith a metal tube, comprising:laser welding means for laser weldingabutment portions of abutting side edges of a metal tube to seal saidmetal tube; and optical fiber guide means for guiding at least oneoptical fiber into said metal tube while said metal tube is maintainedunder traction, said optical fiber guide means comprising a guide tubeinserted into said metal tube for guiding said at least one opticalfiber into said metal tube; said guide tube being provided across awelding position of said welding means; and whereinsaid welding meansfurther comprises position adjusting means for positioning said abutmentportions of said metal tube to a predetermined position with respect toa laser beam radiation position and a path line of said metal tube. 12.An apparatus for manufacturing an optical fiber cable covered with ametal tube, comprising:welding means for welding abutment portions ofabutting side edges of a metal tube to seal said metal tube; opticalfiber guide means for guiding at least one optical fiber into said metaltube while said metal tube is maintained under traction, said opticalfiber guide means comprising a guide tube inserted into said metal tubefor guiding said at least one optical fiber into said metal tube; saidguide tube being provided across a welding position of said weldingmeans; and position adjusting means for adjusting a position of saidguide tube relative to said welding position of said welding means.